1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device, and more particularly to a method by which a surface area of a silicon material used in a semiconductor device is increased.
2. Description of the Related Art
A silicon film is widely used as a charge storage electrode for a capacitor used in a semiconductor device, such as a capacitor of a stacked-type memory cell used in a dynamic random access memory (DRAM). In order to realize a highly-integrated semiconductor device by reducing the size of each memory cell, it is necessary to reduce the size of each capacitor without decreasing the capacitance of the capacitor. Accordingly, some techniques for increasing an area of a charge storage electrode for a capacitor, i.e., a surface area of a silicon film are suggested.
In some conventional semiconductor devices, when a silicon film is deposited by chemical vapor deposition (CVD), a surface of the silicon film is made uneven by adjusting the deposition temperature, whereby an area of an electrode for a capacitor is increased. One example of such conventional semiconductor devices is disclosed in H. Watanabe et al., Sym. on VLSI Tech. page 873 (1990). FIG. 7 is a graph showing the relationship between a deposition temperature of a non-doped silicon film and a capacitance of a capacitor which has the deposited non-doped silicon film as a charge storage electrode. As can be seen from FIG. 7 that the surface area of the non-doped silicon film is remarkably increased when the deposition temperature is within plus or minus 0.4.degree. C. centered at 550.degree. C.
However, according to the above prior art technique, the deposition temperature suitable for increasing the surface area of the silicon film falls within a narrow range, i.e., within plus or minus 0.4.degree. C. centered at 550.degree. C. Accordingly, at a temperature out of the range, the surface of the silicon film is not made largely uneven. It is difficult to adjust the deposition temperature within such a narrow range. The degree of unevenness formed at the surface of the silicon film varies depending on the concentration of impurities contained in the deposited silicon film. For the above reasons, the prior art technique has a problem in that a capacitance of a capacitor cannot be increased with good reproducibility.